Remove common object from js array and create new js array [closed]

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You could use reduce in combination with a Map for keying your data:

const data = [ { "id": 1, "item": { "id": 1, "name": "itemA" } }, { "id": 2, "item": { "id": 1, "name": "itemA" } }, { "id": 3, "item": { "id": 2, "name": "itemB" } }  ];

const [map, dupes] = data.reduce(([map, dupes], obj) =>
    map.has(obj.item.id) ? [map, dupes.concat(obj)] : [map.set(obj.item.id, obj), dupes]
, [new Map, []]);

const uniques = [...map.values()];

console.log(uniques);
console.log('dupes:');
console.log(dupes);

After reading your comments, it seems you want to reject anything that has a duplicate, so not even keeping one original. So then the code could be:

const data = [ { "id": 1, "item": { "id": 1, "name": "itemA" } }, { "id": 2, "item": { "id": 1, "name": "itemA" } }, { "id": 3, "item": { "id": 2, "name": "itemB" } }  ];

const map = new Map(data.map(obj => [obj.item.id, []]));
data.forEach(obj => map.get(obj.item.id).push(obj));
const uniques = [].concat(...[...map.values()].filter(arr => arr.length === 1));
const dupes = [].concat(...[...map.values()].filter(arr => arr.length > 1));

console.log(uniques);
console.log('dupes:');
console.log(dupes);

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